Chapter 3: Plant Kingdom

Q1Written answer

Why are bryophytes called the amphibians of the plant kingdom?

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Worked solution

They inhabit two well-defined habitats i.e. land and water.

b) Bryophytes can complete their life cycle without water; water is required for fertilisation,

c) Water also plays an important role in dehiscence of antheridium and archegonium.

d) As it lacks proper vasculature, water conduction occurs through capillary action.

Hence a thin film of water is required on land, for survival

Q2Written answer

The male and female reproductive organs of several pteridophytes and gymnosperms are comparable to floral structures of angiosperms. Attempt to compare the various reproductive parts of pteridophytes and gymnosperms with reproductive structures of angiosperms.

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Reproductive parts of pteridophytes and gymnosperms

Reproductive structures of angiosperms

Strobili/cone

Microsporophyll

Megasporophyll

Microsporangium

Megasporangium

Flower

Stamen

Pistil/Carpel

Anther

Ovule

Q3Written answer

Heterospory i.e., the formation of two types of spores – microspores and megaspores is a characteristic feature in the life cycle of a few members of pteridophytes and all spermatophytes. Do you think heterospory has some evolutionary significance in the plant kingdom?

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Heterospory led to in situ embryo development. The embryo derives nutrition from the female gametophyte and is better protected. Heterospory led to the evolution of seed habit, which helped the plants to flourish and tide over long periods of unfavourable conditions.

Q4Written answer

How far does Selaginella, one of the few living members of Lycopodiales (pteridophytes), fall short of seed habit?

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Selaginella produces macro and microspores. The megaspores and microspores germinate and produce female and male gametophytes. The embryo was retained within the female gametophyte up to the development of rhizophore, roots and leaves only. Hence, there is no complete retention of an embryo. The seeds of Selaginella and Lycopodium failed to develop protective covering called the integument.

Q5Written answer

Each plant or group of plants has some phylogenetic significance concerning evolution: Cycas, one of the few living members of gymnosperms is called as the ‘relic of past’. Can you establish a phylogenetic relationship of Cycas with any other group of plants that justifies the above statement?

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Cycas is the connecting link between Gymnosperms and Pteridophyte. They show similarities with pteridophytes like flagellated antherozoids, circinate ptyxis, megasporophyll is leaf-like, presence of archegonia etc.

Q6Written answer

The heterosporous pteridophytes show certain characteristics which are the precursor to the seed habit in gymnosperms. Explain.

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Worked solution

Genera like selaginella, Sylvania, Marsilea etc., produce two kinds of spores. Micro and macrospores are known as heterosporous.

(i) Evolutionary heterospory

ii) In-situ development of the embryo within the female gametophyte.

iii) The decrease in the number of megaspores to one.

Q7Written answer

Comment on the lifecycle and nature of a fern prothallus.

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1. Fern shows diplo-haplontic life cycle.

2. Diploid sporophyte represents the dominant, independent, photosynthetic plant body.

3. The sporophyte bears sporangia which produce spores by meiosis.

4. These spores germinate to form free-living prothallus, which represents a gametophyte.

5. Sexual reproduction: syngamy results in the formation of a diploid zygote. Zygote germinates into a diploid sporophyte.

Prothallus:

1. It represents the gametophytic phase.

2. Multicellular, independent, green, photosynthetic thallus.

3. It needs damp and shady places.

4. Bears sex organs, rhizoids and food-laden parenchymatous cells.

Q8Written answer

How are the male and female gametophytes of pteridophytes and gymnosperms different from each other?

Solution;

Pteridophytes

Gymnosperm

Male gametophytes are the anthurium

Cone may or may not be present

Motile male gametes are produced

Female egg not enclosed in an ovule

Antheridium absent

Cones distinctive feature

Non-motile gametes

Neck canal cells are absent

9. In which plant will you look for mycorrhiza and coralloid roots? Also, explain what these terms mean.

Solution;

Mycorrhiza can be seen in Pinus and coralloid root in Cycas.

Mycorrhiza – system association between the roots of higher plants & fungi. Fungi help the plants in the absorption of nutrients, especially phosphorus in return, they go to the shelter.

Coralloid roots – when the roots of higher plants like Cycas show association with BGA. It is also an example of a symbiotic association

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